Health campaigners are urging the International Olympic Committee (IOC) to ban junk food and fizzy drink brands from future sporting sponsorship deals in a critical new report which says the committee has squandered the chance to create a positive health legacy from the London 2012 Games.

The Obesity Games report, published by The Childrens' Food Campaign (CFC), found that corporate sponsorship accounts for less than 10% of the total funding for the London 2012 Games, while fast food sponsors contribute only about 2% of the IOC income. Yet the major sponsors Coca-Cola, McDonald's and Cadbury are given an unrivalled platform to promote their unhealthy brands and products, it says.

The CFC is calling for the IOC to help tackle rising obesity levels by setting conditions on promoting healthy eating in their sponsorship deals and for junk food brands to be excluded.

The findings will trigger fresh criticism of the stranglehold on food and drink at the Games held by sponsors Cadbury, McDonald's (its largest restaurant in the world is in the Olympic Park) and Coca-Cola, which is expected to serve 23m soft drinks at the Games due to its near-monopoly at Olympic venues.

CFC co-ordinator Malcolm Clark said: "The Olympics have become a celebration of 'big'. For the junk food companies who sponsor the Games, that means big restaurants, big audiences, big brand value, big profits. But for children that could also mean bigger waistlines and bigger health problems later in life."

He said the IOC could decide to cut out the top-tier category of food and soft drink partners entirely and lose little more than 2% of its total income.

Coca-Cola said: "As one of the longest, continuous sponsors of the Olympic movement, we are proud that we are able to use our sponsorship to enable millions of people to experience the Games and believe we have a valid role to play. As well as sharing expertise, our financial support helps to stage London 2012, and without the support of the presenting partners the Olympic torch relay would not be able to take the magic of the Games to people in their own communities.

"People consume many different foods and drinks, so no one single food or drink alone is responsible for people being overweight or obese. We believe all of our drinks can be enjoyed as part of an active, healthy lifestyle that includes a sensible, balanced diet and regular physical activity."

McDonald's said: "Sponsorship is essential to the successful staging of the Olympic and Paralympic Games and we're proud of our involvement with London 2012."

Ian Barber, the director of communications at the Advertising Association, said: "Much analysis has been done about advertising's link with our obesity problem. Prof David Buckingham – an independent expert – sums it up when he says, 'the impact, if any, is small'."